The invention relates to a double O-ring sealing arrangement utilized to keep hydraulic fluid pressure operating on one side of a first O-ring from being contaminated by air operating against an opposing side of the second O-ring.
In piston arrangements used for braking systems, hydraulic fluid is utilized to act on the face of the piston to apply or release the brake in response to the pressure of the fluid applied. Normally, this pressure acts against the bias of springs in the brake control system. When the piston is to be activated to apply the brake, high pressure fluid is applied to an end face of the piston. When the brake is to be released, the pressure of the hydraulic fluid applied to the end face of the piston is considerably reduced, and if reduced below atmospheric pressure, air can leak past the fluid seals on the edges of the piston and contaminate the hydraulic brake fluid. Air in the brake fluid lines causes a loss of control of the brake due to tee fact that air is compressible, whereas the fluid is not. Thus, the brake pedal cannot apply the brake properly.
It is an object of this invention to provide a particular sealing arrangement which eliminates the leakage of air around the sealing arrangement, and thus avoids contamination of the hydraulic brake fluid. When air gets into the brake fluid, the brakes become relatively unusable due to the compressibility of the air.
The present invention utilizes a double O-ring sealing arrangement for a brake piston which prevents air from being introduced into the hydraulic system of the hydraulic pressure drops below atmospheric pressure. Under special conditions and in some brake systems, when hydraulic brakes are utilized, the hydraulic pressure will drop below atmospheric Pressure upon release of the brakes. Note my prior U.S. Pat. No. 4,691,520 of Sept. 8, 1987 entitled Hydraulic Brake System. At such time, atmospheric pressure surrounding the piston has a tendency to bypass and leak around the sealing arrangement and contaminate the hydraulic fluid.
Applicant has devised a double O-ring sealing arrangement which eliminates commingling of the air and the hydraulic fluid which activates the piston. The double O-ring sealing arrangement comprises two O-ring seals provided circumferentially about the piston and spaced from one another to provide a storage-buffer chamber therebetween.
This storage-buffer chamber receives high pressure hydraulic fluid when a high pressure hydraulic fluid is applied to the brake piston end face to apply the brakes. When the brakes are to be released, the high pressure hydraulic fluid applied to the end face may be reduced below atmospheric pressure. At the time this reduction in hydraulic fluid pressure at the end face of the piston takes place, the storage-buffer chamber is kept filled with high pressure fluid to thus Provide an effective sealing pressure force about the second O-ring. At this time the second 0-ring will have atmospheric air pressure on one side thereof and the storage-buffer chamber pressure on the other side thereof. Thus, there will be no tendency for the air at atmospheric pressure to leak past the O-ring into the reduced Pressure of the hydraulic fluid at the piston end face which is now at below atmospheric pressure, and thus contamination is avoided.
The double O-ring sealing arrangement comprises a first O-ring seal located longitudinally along the side of the skirt of of the piston and spaced from a second O-ring seal. The first O-ring seal sits in a V-shaped channel on the piston. The V-shaped channel runs radially around the piston and has a first outwardly sloping side ramp facing the end face of the piston and a second outwardly facing side ramp extending away from the end face of the piston. These two sloping faces define the V-shaped recess.
A passageway is located in the sloping face farthest from the end face of the piston. This passageway leads to the storage-buffer chamber which, at an end opposite the first O-ring, contains second O-ring. On the side of the second O-ring, not facing the storage-buffer chamber in the direction of the end face of the piston, is the normal clearance way connected to atmospheric air. When high pressure hydraulic fluid is applied to the end face of the piston, this pressure causes the first O-ring to deform and move away from the first outwardly facing ramp. As the first O-ring deforms, O-ring contact with the first ramp is lost, so that high pressure fluid leaks around the first O-ring through the passage into the storage-buffer chamber. When the pressure in the storage-buffer chamber equals the pressure of the hydraulic fluid operating on the end face of the piston, the first O-ring will move back into contact with the first ramp and trap fluid in the storage-buffer chamber. The reason for the first O-ring moving back to its original position, is that the pressures on both sides of the O-ring are equal, thus producing no net force thereon and the normal tendency for a rubber O-ring is to be deformed by pressure and to resume its normal O-ring configuration when unequal pressures are no longer being applied. Thus, as the hydraulic pressure is subsequently lowered at the end face of the piston with the concurrent movement of the first O-ring to close off the passageway, the storage-buffer chamber maintains the high pressure therein, which high pressure acts on one side of the second O-ring to prevent air from leaking into the hydraulic fluid. This is true because the pressure then in the storage-buffer chamber is high compared to the atmospheric pressure of the air surrounding the brake piston.
As the pressure in the storage-buffer chamber is high compared to the atmospheric pressure of the air on the other side of the second O-ring, some leakage of the hydraulic fluid past either O-ring may occur. Accordingly, the storage-buffer chamber is made flexible, so that there will be sufficient hydraulic fluid therein to maintain pressure, regardless of the small leakages that might take place past either O-ring.
One method of increasing the volume of the storage-buffer chamber is by connecting the storage-buffer chamber with an auxiliary storage chamber having a deformable wall or walls. This auxiliary storage chamber can be a hollowed out area in a portion of the piston itself.
When high pressure hydraulic fluid is applied to the end face of the piston, leakage of this high pressure fluid around the sides of the piston to cause the first O-ring to move is inherent. Additionally, the end face of the piston can be configured such that when the high pressure hydraulic fluid is applied to the end face of the piston, a portion of the piston deforms to increase the amount of leakage of high pressure hydraulic fluid into the buffer chamber. This deformation is essentially longitudinal and not axially.
The above double O-ring sealing arrangement can be utilized on pistons in brake systems where the skirt of the piston itself actuates the pressure plate of the brake.
In systems wherein there is an intermediate member between the piston and the pressure plate, a different part of the piston deflects under pressure to provide increased buffer chamber volume.
This double O-ring sealing arrangement provides the necessary sealing environment for this type of structure.
It is thus seen that the invention provides a double O-ring sealing arrangement wherein a storage-buffer chamber is interposed between two O-ring seals so that air pressure on one side of one seal is not allowed to contaminate the hydraulic fluid on the other side of the other seal when the hydraulic fluid is reduced to below atmospheric pressure.